A man in soldier's uniform blows himself up at a military parade rehearsal; defense minister, chief of staff are present but unhurt.

SANAA - A suicide bomber with explosives strapped under his uniform killed more than 90 people at a military parade rehearsal in the Yemeni capital Sanaa on Monday, an attack which will alarm Washington as its involvement in the front-line state deepens.

The bombing also wounded about 200 people, officials said, making it the bloodiest single incident in the city in recent years.

Yemen's defense minister and chief of staff were both present at the rehearsal for Tuesday's National Day parade but neither was hurt. A police source said he could not rule out the bombing was an attempt to assassinate them.

Weakened by an uprising that eventually toppled former leader Ali Abdullah Saleh, Yemen's government has lost control over whole swathes of the country, allowing militants to overrun several towns in the southern province of Abyan.

The attack, along with an ambush on Sunday on a US military training team, indicated their campaign could be entering a dangerous new stage.

The United States sees Yemen as a vital front in its global war on Islamic militants and is increasing its military support for the government of Yemeni President Abd-Rabbu Mansour Hadi.

A US military instructor was seriously wounded in Sunday's ambush, claimed by militant group Ansar al-Sharia (Partisans of Islamic Law), which is affiliated to al-Qaida in the Arabian Peninsula (AQAP).

The same group also claimed responsibility for the military parade suicide attack, saying it was in response to the "crimes" of the security forces, who are fighting to dislodge militants from their strongholds in Abyan.

Scenes of carnage

The explosion in Sanaa's Sabaeen Square left scenes of carnage, with bloodied victims and body parts strewn across the 10-lane road where the rehearsal was held on Monday morning, not far from the presidential palace.

The Defense Ministry said at least 90 soldiers were killed and 222 wounded.

"We had just finished the parade. We were saluting our commander when a huge explosion went off," said soldier Amr Habib. "It was a gruesome attack. Many soldiers were killed and others had their arms and legs blown off."

One investigator said preliminary findings suggested the suicide bomber was a rogue soldier rather than a man in a disguise.

"The suicide bomber was dressed in a military uniform. He had a belt of explosives underneath," said a man who identified himself as Colonel Amin al-Alghabati, his hands and uniform flecked with blood.

The usual security procedure for such an event would involve checks being made on the soldiers at their bases before they are transported to the site of the parade in army vehicles.

The wounded were ferried to hospital in taxis.

"Most of the injuries are to the head, we have dozens paralyzed. We expect the death toll to rise. Most of the injured here are boys in their teens. Sanaa's hospitals are overwhelmed," said doctor Mohsen al-Dhahari.

In response to two days of violence, Hadi sacked two senior commanders and allies of his predecessor Saleh, whom he replaced in February.

One of them, a nephew of Saleh's, was the head of national security, an intelligence gathering unit that works closely with the CIA.

The impoverished state has seen a spate of deadly attacks since Hadi took office saying he would extinguish an Islamist insurgency, which until now has been concentrated in the south.

At least seven militants and seven soldiers were killed in clashes when Islamist fighters attacked an army position near the southern town of Zinjibar on Monday, residents and a local official said.

Yemeni troops closed in on the southern militant-held town of Jaar on Sunday in heavy fighting, part of a new US-backed offensive launched earlier this month to regain control of territory and towns seized by Ansar al-Sharia.

The parade was scheduled for Tuesday to mark the unification of north and south Yemen, previously separate states, which were merged in 1990.